1. Field of the Invention
The present invention relates to a control method of and apparatus for material charging at the top of a blast furnace where material can be charged precisely at target speed when material is charged into the furnace from a top bunker of bellless furnace top charging equipment.
2. Description of the Prior Art
In the operation of blast furnace, blast furnace charging materials are stored in a bunker according to the kinds of materials the will be charged into the blast furnace. Firstly furnace charging materials of given kinds and given quantities are sent to a weighing hopper depending on the composition of the product to be made and charging schedules, and then material charging is carried out according to a given charging schedule and charging speed at the top of the furnace ultimately.
Generally speaking, a blast furnace operation shall be carried out efficiently using the inherent heat and reducing capabilities which gas possesses, while gas distribution and gas permeability within the blast furnace, depending on the properties of material to be charged into the blast furnace and material charge conditions to a great extent, are maintained under the proper condition.
Therefore, bellless blast furnace top charging equipment is adopted as furnace top charging equipment of a blast furnace which can improve control labity of material distribution within the furnace and can increase the degree of freedom of the material distribution.
FIG. 21 is an explanation diagram of material charging method in a bellless type blast furnace.
In FIG. 21, material M having been stored in advance in a furnace top bunker 10 is charged into a blast furnace 14, being controlled at a given charging speed by a flow rate control gate 12 provided at the lower end of the furnace top bunker 10.
Moreover, at the time of charging the material M into the blast furnace 14, concentric dumping pattern 18 is set and the material is charged into the upper surface in the side of the blast furnace 14, by using and circulating a distributing chute 16 whose starting and stopping of rotation and the rotation speed are controlled. That is, the distributing chute 16 arranged within the blast furnace 14 below the flow rate control gate 12, so that the locus of the top of the distributing chute 16 coincides with the dumping pattern 18.
Moreover, the angle of inclination of the distributing chute 16 is also controllable during rotation at the given rotation speed.
Therefore, regarding the material charging using such a distributing chute 16, the material distribution within the blast furnace 14 can be regulated by controlling the rotational speed and the inclination angle of the distributing chute 16.
In order to form the given material distribution within the blast furnace 14 in the case of charging the material into the blast furnace 14 by the above-mentioned method, it is important to secure the accuracy of a "charge stop" in which the time points of dumping start point S and dumping end point E in the dumping pattern 18 coincide with those of the start and stop of practical material dumping respectively, the control accuracy of charging speed, and the improvement of the positioning accuracy of the dumping start point S and the dumping end point E.
In order to secure the accuracy of the above "charge stop", it is usually required that a flow rate control gate 12 is opened at a given opening at the time of reaching the top of the distributing chute 16 to the dumping start point S in the dumping pattern 18, and the distributing chute 16 is rotated by an angular velocity omega and its inclination angle theta is varied. After being rotated by a predetermined number of times, the top of the distributing chute 16 coincides with the dumping end point E at the dumping pattern 18, and simultaneously the material dumping is completed.
But, it is very difficult to rotate the distributing chute 16 a predetermined number of times so that its top coincides with the dumping end point E, and to control "the charge stop" so as to complete the practical material dumping simultaneously.
Namely, when the degree of opening of the flow rate controlling gate 12 is made too small, the material M remains in the furnace top bunker 10 even if the rotation of prescribed times is finished, and then the condition of overchute occurs where the distributing chute 16 has to be rotated more times than prescribed in order to charge the total quantity of the material M.
On the contrary, if the degree of opening of the flow rate control gate 12 is made too large, the material M becomes consumed before the top of the distributing chute 16 has reached the predetermined dumping end point E, and the condition of underchute occurs where the distributing chute 16 cannot be rotated by the prescribed times.
Irrespective of the overchute condition and the underchute condition, the balance of the locus of the material dumping in the circumferential direction inside the furnace is disturbed, and a predetermined material distribution in the furnace cannot be formed.
The above-mentioned charge stopping is controlled, for example, in Japanese Utility Model Publication No. 38424/1984 as follows.
First, the completion of the material dumping from the furnace top bunker 10 is determined according to, for example, an acoustic sensor of vibration acceleration pickup type installed in the vicinity of the flow rate control gate 12 and the change of dumping ratio of a load cell installed on the furnace top bunker 10. Thus the numbers of rotations required for the actual material dumping can be determined.
Next, the difference between the predetermined of rotations and the actual number of rotations is determined, and overchute or underchute is determined.
If it is overchute, the degree of opening of the flow rate control gate 12 for the next dumping would be manually made larger by an amount corresponding to the deviation in the last dumping. On the contrary, if it is underchute, the degree of opening would be manually made smaller.
Also, a method of controlling by learning regulation of the degree of opening is known as described in Japanese patent application laid-open No. 47506/1981.
In all of the methods of controlling the accuracy of the charge stopping in the prior art as above described, the degree of opening of the flow rate control gate at the next dumping is regulated based on actual results of the numbers of rotations.
FIG. 22 shows relation between the material dumping speed and the dumping completion time in the case of controlling the material dumping according to these methods in the prior art. Axis of abscissa shows time, and axis of ordinate shows dumping speed at the time of dumping the material from the furnace top bunker.
In FIG. 22, solid line shows an example when charge stopping accuracy is high, and the material dumping from the furnace top bunker is completed at the determined dumping time A.
On the other hand, broken line shows an example where dispersion of the weighing accuracy in the case of weighing the material upstream of a furnace top bunker causes the outer disturbance of the material dumping control. In this example, the material weight is small and underchute takes place. Therefore, when the actual number of rotations of the distributing chute is less than that prescribed as above, the control lessens the degree of opening at next dumping.
Also, the one dot chain line shows an example where changes of physical attributes, e.g., kinds of material (brand), grain size, moisture or the like cause the outer disturbance. In this example, the dumping speed is slow and overchute takes place. Therefore, when the actual circling number of rotations of the distributing chute is more than that prescribed above, the control enlarges the degree of opening in the next dumping.
Further, various techniques are also disclosed as techniques for improving the accuracy of the dumping speed of material, position of the dumping start point and position of the dumping end point.
For example, in Japanese patent application laid-open No. 47506/1981, a technique is disclosed where the next degree of opening of the flow rate control gate valve is learned and calculated based on information of the chute rotation numbers accumulated in the past and the last degree of opening of the flow rate control gate valve, the rotation speed being kept constant, or the rotation speed is learned and calculated, the degree of opening of the flow rate control gate valve being kept constant.
According to the technique having been disclosed in Japanese patent application laid-open No. 47506/1981, even if variation of the physical properties of materials or the mechanical wear of the flow rate control gate valves and the chute guides occurs, the accuracy of the material dumping speed into the blast furnace can be improved by equally dumping materials at the given rotation number exactly by learning.
Also Japanese utility model publication No. 38424/1984 discloses a technique where in a material charging device of a bellless type blast furnace for charging materials through a plurality of furnace top bunkers, assembled chutes and a slewing chute leading into the blast furnace. A mass meter and a pressure meter are provided on the furnace top bunkers, and an acoustic sensor or a vibration meter is provided below the assembled chutes. Detection of the dumping completion and measurement of the dumping duration time are carried out using the acoustic sensor or the vibration meter. The set dumping duration time is compared with the actual dumping duration time and opening degree of flow rate control gate at the time of next material dumping is controlled.
According to the technique disclosed in Japanese utility model publication No. 38424/1984, the actual dumping duration time having high accuracy can always be obtained and the dumped material distribution within the blast furnace can be adequately controlled without being influenced by the clogging of material in the bunkers, the kinds of materials and the variation of physical properties of the materials.
Moreover, when the distributing chute 16 transfers between circular rings of a dump pattern 18, the distributing chute 16 must be inclined smoothly, in order not to vibrate to the material M on the distributing chute 16, and the distributing chute 16 must be inclined rapidly, in order not to dump useless materials onto the locus of the transfer between the circular rings.
Conventionally, the control of the tilted operation of the distributing chute 16 has been carried out by a method shown in FIG. 23 and FIG. 24.
FIG. 23 shows the case that the top end of the distributing chute 16 transfers from the outer circular ring "a" with the inclination angle of the distributing chute 16 being constituted by "a" degrees to the inner ring "b" with the inclination angle being constituted by "b" degrees. Also FIG. 24 shows the relation between the inclination angle (distance deviation) and the inclining speed of the distributing chute 16 during transfer.
That is, the distributing chute 16 is accelerated by the highest speed Vmax at the starting time point transferring from the inclination angle "a" degrees, and when the inclination angle deviation (a-b) between transfer of the distributing chute 16 has reached 1 degree, the inclining speed is reduced to 1/10 of the highest speed Vmax. Further, at the time point of the angle deviation between transfer reaching 0.1 degree, that is, at the time point reaching 0.1 degree before the inner circular ring "b" of the dump pattern 18, the power supply is interrupted and the inclined motion of the distributing chute 16 is braked and stopped. Thus the transfer from the outer circular ring "a" to the inner circular ring "b" is carried out. Moreover, the generally applied values shall be represented regarding numerical values of the inclining speed and the inclination angle of the distributing chute 16.
However, the material charging control method at the top of the blast furnace as above described has the following problems.
Usually, materials should be weighed at the upstream of the furnace top bunker, but the material weight of the furnace top bunker varies slightly every dump causing inaccuracies. Therefore it is impossible to control the material dumping with good accuracy in response to its weight variation.
Moreover, the dumping speed and positions of the dumping start point and the dumping end point vary depending on the variation of grading of material and quantity of moisture included in the material and physical properties. Thus the control of the material dumping is difficult and imprecise.
That is, the grading of such material, moisture included in the material and physical properties of the material vary with time during the material dumping. Therefore, when the material is to be dumped into the blast furnace, the variation of the grading of such material, moisture included in the material and physical properties must be determined by real time, and the degree of opening of the flow rate controlling gate or the like must be regulated.
Nevertheless, regulation of the degree of opening of the flow rate controlling gate and correction of the opening degree regulation are carried out for each successive material dumping as described in the above Japanese patent application laid-open No. 47506/1981 and utility model publication No. 38424/1984. That is, even if the characteristics of the material dumping control vary, this cannot be detected before the material dumping of one time has been completed. Moreover, detection of variation of the material dumping control can only be at the time of next material dumping
Further, the conventional technique as described above is not satisfactory regarding the point of keeping a suitable gas stream distribution. There is a relationship between the dumping speed of material being dumped into a blast furnace and the grain diameter of the material as follows. EQU (dumping speed V).times.(grain diameter D)= approximately constant(1)
That is, the smaller the grain diameter D of material being dumped is, the higher the dumping speed V becomes. As a result, a great deal of materials are dumped and piled up, so gas flow becomes smaller. On the other hand, the larger the grain diameter D of material being dumped is, the lower the dumping speed V becomes, and materials being dumped into a blast furnace become less. so gas flow becomes larger.
Therefore, even if there is a slight variation in the grain diameter of material being dumped into a blast furnace, gas flow distribution from furnace walls up to the furnace center within the blast furnace varies greatly.
Moreover, even if the dumping speed for materials being dumped can be controlled at a definite level, there is a problem that gas flow distribution in the blast furnace cannot be maintained correctly in the case of variation of grain diameter of materials being dumped.
For example, if the distribution of grain diameters of materials being dumped into the blast furnace is in that fine grains are on the side of furnace walls and coarse grains are on the side of the furnace center, the gas flow distribution will be strongly shifted to the side of the furnace center.
Even if the charge stopping accuracy is higher, since the drop volume of materials on the locus of bellless dump pattern is varied in the case of variation of the dumping speed the desired distribution of materials in the furnace cannot be
Moreover, concerning the feedback control in which the degree of opening of the flow rate control gate at the dumping is determined by the actual results of dumping of the last time, it cannot be guaranteed that the actual results of material weights and dumping speeds of the last time can be correctly reproduced in the next dumping.
Further, regarding the above-mentioned control method of the distributing chute inclined operation, the distributing chute 16 and the material M on the distributing chute 16 are subjected to large vibration, as acceleration is made at the highest speed Vmax suddenly when the transfer of the distributing chute 16 starts from the outer circular ring "a". This vibration occurs when the inclining speed is suddenly reduced to (1/10) Vmax at the same time the inclination angle deviation reaches 0.1 degree.
Also since the distributing chute 16 is inclined at the position of (1/10) Vmax after the deceleration time, approximately six seconds are required to reach the position of the angle deviation 0.01 degree between the transfer, and the transfer locus of the distributing chute 16 becomes the length of approximately one rotation as shown in FIG. 23. Consequently, the distributing chute 16 dumps large amounts of undesired material M onto the transfer locus.
Further, as the speed of (1/10) Vmax is too large to stop the distributing chute 16 suddenly, the top of the distributing chute 16 does not stop on the inner circular ring "b" exactly, even if the distributing chute 16 is braked at the time point reaching 0.1 degree before the inner circular ring "b" of the dump pattern 18, and the position accuracy of the distributing chute 16 for the inner circular ring "b" is low and limited to plus or minus 0.1 degree at most.
Thus, in the conventional control method of the distributing chute inclined operation, as the distributing chute 16 and the material M on the distributing chute 16 are subjected to vibration, and large amounts of undesired materials M are dumped between the circular rings "a", "b", and further the position accuracy of the circulating chute 16 for the inner circular ring b is low, a problem occurs in that the desired distribution of materials in the furnace cannot be obtained.